1. Field of the Invention
This invention relates to a camera having a connector common to a flash bulb unit and an electronic flash unit, and particularly to a camera which receives the shutter time setting signal from the electronic flash unit and automatically sets the shutter time to an electronic flash tuning time, and to an underwater camera system including an underwater flash bulb unit, an underwater electronic flash unit and an underwater camera.
2. Description of the Prior Art
A synchroconnector for an underwater camera (e.g. NIKONOS III manufactured and sold by Nippon Kogaku K. K. of Japan) and an underwater flash unit which is now commercially available will first be described by reference to the accompanying drawings. Referring to FIGS. 1A and 1B, the conventional synchronizing connector for an underwater camera comprises a socket 1 shown in FIG. 1A and a plug 100 shown in FIG. 1B. The socket 1 is provided on the underwater camera, and the plug 100 is attached to the underwater flash unit. In order that this synchronizing connector may be usable both with an underwater electronic flash unit and an underwater flash bulb unit, the socket 1 is provided with a X contact terminal 2 for synchronizing the underwater electronic flash unit, a FP contact pin terminal 3 for synchronizing the underwater flash bulb unit, a ground contact pin terminal 4 and a projection 5 for correctly positioning the plug 100. The plug 100 is provided with spring-like terminals 102, 103, 104 forming holes into which the pin terminals 2, 3, 4 of the socket 1 may be inserted, and a positioning cut-away 105 corresponding to the projection 5. Clamp means effective when the socket 1 and the plug 100 have been coupled together and the waterproof mechanism in the connector are not shown in the drawing.
Description will now be made of the case in which an underwater flash bulb unit is used as an underwater flash unit. The underwater flash bulb unit, as shown in FIG. 2, is provided with a flash bulb 10, a battery 11 having its positive pole connected to one terminal of the flash bulb, a resistor 12 connected to the negative pole of the battery 11, a capacitor 13 parallel-connected to the serial circuit of the battery 11 and the resistor 12, a terminal 103 of the plug 100 connected to the negative pole of the battery 11 through the resistor 12, and a ground terminal 104 of the plug 100. When the plug 100 is coupled to the socket 1 of the underwater camera, the terminals 102, 103 and 104 come into contact with the pins 2, 3 and 4, respectively. When, by the release operation of the underwater camera, the synchronizing signal in the underwater camera is transmitted to the underwater flash bulb unit, that is, the terminals 103 and 104 are short-circuited, the underwater flash bulb 10 emits flashlight. Of course, at this time, the terminal 102 and pin terminal 2 for the electronic flash unit are ineffective. Where an underwater electronic flash unit is used as an underwater flash unit, a light emission start signal is sent from the camera side to the underwater electronic flash unit through the terminals 102, 104 of the connector and the pin terminals 2, 4 that is, the terminals 102 and 104 are short-circuited and flashlight is emitted. At this time, the terminal 103 and pin 3 for the underwater flash bulb unit perform no function.
However, in recent years, underwater flash bulb units have scarcely been used and thus the pin 3 of the connector for flash bulb has become substantially unnecessary.
On the other hand, recently, the advance of the electronic instrumentation of cameras has brought about wide use of electric shutters provided with a tuning shutter time setting circuit which, when an electronic flash unit is used, automatically sets the shutter time to an electronic flash tuning speed by a tuning shutter time setting (TSTS) signal from the electronic flash unit side. Accordingly, where such an electric shutter is used in an underwater camera, a pin terminal and spring-like terminal for X contact, a pin terminal and spring-like terminal for shutter time setting signal, and a pin terminal and spring-like terminal for ground become necessary in a connector (hereinafter referred to as the new type connector) for connecting together an underwater electronic flash unit designed to produce a tuning shutter time setting signal (hereinafter referred to as the new type underwater electronic flash unit) and an underwater camera designed such that the shutter time is automatically set to a tuning speed by the shutter time setting signal (hereinafter referred to as the new type underwater camera). However, providing interchangeability between new and old connectors so as to render the new type underwater electronic flash unit usable in conjunction not only with the new type underwater camera but also with an underwater camera (hereinafter referred to as the old type underwater camera) provided with a connector (hereinafter referred to as the old type connector) equipped with the above-described pin terminals 2, 3, 4 and spring-like terminals 102, 103, 104 for X contact, FP contact and earth, respectively, and conversely to render an underwater electronic flash unit having the old type connector (hereinafter referred to as the old type underwater electronic flash unit) usable in conjunction with the new type underwater camera as well would be preferable to persons who already possess the old type underwater cameras and the old type underwater electronic flash unit. To achieve such interchangeability, the positional relations among the pin terminals and the spring-like terminals and the projection and the cut-away may be determined so as to be identical between the old type connector and the new type connector. That is, in the new type connector, the pin 3 of FIG. 1A may be connected to the tuning shutter time setting circuit of the camera and the terminal 103 of FIG. 1B may be used as the tuning shutter time setting signal terminal of the new type electronic flash unit. However there is the following problem. The existing electric shutter is designed such that the shutter time setting signal is a positive electrical signal. In the new type underwater electronic flash unit, in order to be compatible with an underwater camera incorporating such an electric shutter therein, it is necessary that a positive potential signal as the shutter time setting signal should be produced at the terminal 103 of the new type connector, whereas in the conventional underwater flash bulb unit, as shown in FIG. 2, a negative potential is applied to the terminal 103 of the old type connector. Therefore, if the plug of the conventional underwater flash bulb unit is, by mistake, coupled to the socket of the new type underwater camera, the possibility will exist that the tuning shutter time setting circuit in the camera will malfunction or be damaged. Reversely connecting the battery 11 in the underwater flash bulb unit would also be conceivable, but the positive potential produced thereby at the terminal 103 is a relatively great voltage of the order of 3V or higher while, on the other hand, the shutter time setting signal is a relatively small voltage of the order of 1V or lower and therefore, the above-noted problem would still exist.